Process for producing 2&#39;, 3&#39;-diethy substituted nucleoside derivatives

ABSTRACT

There can be provided an excellent industrial process for producing compounds having sugar-moiety hydroxyl groups or halogen atoms reduced in nucleic acids or in derivatives thereof by allowing O-thiocarbonyl derivatives of sugar-moiety hydroxyl groups or allowing halogenated derivatives in the sugar-moiety, in the nucleic acids or in derivatives thereof to react with any one of hypophosphorous acids (including salts thereof) and phosphites (esters) which are inexpensive, non-toxic and safely usable as radical reducing agents in industrial scale, in the presence of a radical reaction initiator.  
     The process of the present invention is an industrially useful and highly safe process for reducing sugar-moiety hydroxyl groups and halogen atoms in nucleic acids or derivatives thereof (including nucleic acid-related compounds) at low costs.

BACKGROUND OF THE INVENTION

[0001] 1. Field of the Invention

[0002] The present invention relates to a novel process for producingnucleic acid derivatives and in particular to an industrially usefulprocess for reducing sugar-moiety hydroxyl groups and halogen atoms innucleic acids and their derivatives (their related compounds etc.).

[0003] According to the present invention, an intermediate for producingvarious pharmaceutical preparations, for example an intermediate forproducing 9-(2,3-dideoxy-2-fluoro-β-D-threo-pentofuranosyl) adenine(also may be called “FddA” as the abbreviation in the specification) and2′,3′-dideoxyadenosine (also may be called “ddA” as the abbreviation inthe specification) useful as antiviral agents can be producedindustrially advantageously.

[0004] 2. Description of The Related Art

[0005] For dehydroxylation (deoxylation) of sugar-moiety hydroxyl groupsin nucleic acids or in their related compounds, the method of radicallyreducing thiocarbonyl derivatives of such hydroxyl groups has beengenerally used. Further, for dehalogenation of sugar-moiety halogenatoms in nucleic acids or in their related compounds, the method ofradically reducing them has been generally used (for example, see A. G.Sutherland, “Comprehensive Organic Functional Group Transformations”,Vol. 1, A. R. Katritzky, et al., Ed., Pergamon, London, pp. 1-25).

[0006] In the radical reduction described above, tin compounds such astributyl tin hydride are used most generally as radical reducing agents.However, tin compounds when used in industrial production areproblematic in their toxicity during operation, and when used inproduction of pharmaceutical preparations etc., their presence even in atrace amount is not allowable and their use is virtually not possible.Silyl hydride-type compounds such as tris(trimethylsilyl) silane areused as radical reducing agents in some cases, but these silylhydride-type compounds are generally not produced in industrial scale,and even if produced, they are very expensive and very difficult to usein industry.

[0007] In recent years, Barton et al. conducted radical reduction ofthiocarbonyl derivatives and halogen atoms with hypophosphorous acid orsalts thereof or with esters of phosphorous acid (for example, see D. H.R. Barton, et al., Tetrahedron Lett., 33(39), 5709 (1992) and D. H. R.Barton, et al., J. Org. Chem., 58, 6838 (1993)). However, theseliteratures illustrate the radical reduction of only simple hydrocarbonsor sugar derivatives having a few functional groups, and whether thisradical reduction can be applied to complex heterocyclic nucleic acidderivatives was not known.

[0008] Accordingly, there is a need for an industrially advantageous andsafe process applicable widely to nucleic acid derivatives in order toproduce the reduced compound. PROBLEMS TO BE SOLVED BY THE INVENTION

[0009] The object of the present invention is to establish anindustrially useful and highly safe process for producing the reducedcompounds at low costs, wherein sugar-moiety hydroxyl groups and halogenatoms in nucleic acids or in their derivatives (including their relatedcompounds etc.) can be selectively reduced to advantageously produce awide variety of useful nucleic acid derivatives such as intermediatesfor producing the active ingredients (FddA, ddA etc.) in pharmaceuticalpreparations.

SUMMARY OF THE INVENTION

[0010] As a result of their eager study to solve the problem describedabove, the present inventors found that compounds wherein sugar-moietyhydroxyl groups or halogen atoms in nucleic acids and derivativesthereof (referred to collectively as “nucleic acid derivatives”) havebeen reduced can be easily obtained by allowing O-thiocarbonylderivatives of sugar-moiety hydroxyl groups, or halogenated derivativesin the sugar-moiety thereof, to react with any one of hypophosphorousacids (including salts thereof) and esters of phosphorous acid which areinexpensive, non-toxic and safely usable as radical reducing agents inindustrial scale, in the presence of a radical reaction initiator, andas a result, the present inventors found that it is thereby possible toderive a wide variety of useful nucleic acid derivatives industriallyefficiently, to arrive at the completion of the present invention.

[0011] That is, the present invention encompasses the followinginventions.

[0012] (i) A process for producing a nucleic acid derivative representedby the general formula (II):

[0013] wherein B represents a nucleic acid base, R represents a hydrogenatom or a hydroxy group-protecting group, and one of Y′ and X′represents a hydrogen atom and the other represents a hydrogen atom, afluorine atom, a hydroxyl group or a protected hydroxyl group,respectively, which comprises allowing a nucleic acid derivative havingan eliminating group represented by the general formula (I):

[0014] wherein B and R have the same meanings as defined above, and oneof Y and X represents an eliminating group and the other represents ahydrogen atom, a fluorine atom, a hydroxyl group or a protected hydroxylgroup, respectively, to react with at least one compound selected fromhypophosphorous acid (including salts thereof) and esters of phosphorousacid in the presence of a radical reaction initiator. In this reaction,the above eliminating group is reduced and converted into a hydrogenatom.

[0015] In the present invention, the nucleic acid base represented bythe above group B also includes nucleic acid base derivatives. Thenucleic acid base derivatives include e.g. N-acetylguanine,N-acetyladenine, N-benzoylguanine, N-benzoyladenine,2-amino-6-chloropurine and 6-chloropurine.

[0016] (ii) The process according to item (i) above, wherein B is apurine base or a pyrimidine base or a derivative thereof.

[0017] (iii) The process according to any one of the above items,wherein B is any one of hypoxanthine, adenine, guanine, uracil, thymineand cytosine, or a derivative thereof.

[0018] (iv) The process according to item (i) above, wherein R is anyone of a hydrogen atom, an acyl group, an alkyl group, an aralkyl groupand a silyl group.

[0019] (v) The process according to any one of the above items, whereinR is any one of a hydrogen atom, an acetyl group, a benzoyl group and atrityl group.

[0020] (vi) The process according to any one of the above items, whereinthe eliminating group is either a halogen atom excluding a fluorine atomor an O-thiocarbonyl derivative (residue).

[0021] The halogen atom includes the respective atoms of chlorine,bromine and iodine, and the O-thiocarbonyl derivative (residue) includesO-phenoxythiocarbonyl group: PhO(C═S)O—, O-parafluorophenoxythiocarbonylgroup: p-F—PhO(C═S)O—, O-methylthiothiocarbonyl group: MeS(C═S)O—,O-phenylthiothiocarbonyl group: PhS(C═S)O—, and O-imidazolylthiocarbonylgroup:

[0022] (vii) The process according to any one of the above items,wherein one of Y and X is an eliminating group and the other is any oneof a hydroxyl group, an acyloxy group, an alkyloxy group, an aralkyloxygroup and a silyloxy group.

[0023] (viii) The process according to any one of the above items,wherein one of Y and X is an eliminating group and the other is any oneof a hydroxyl group, an acetyloxy group and a benzoyloxy group.

[0024] (ix) The process according to any one of the above items, whereinhypophosphorous acid is in the form of sodium hypophosphite.

[0025] (x) The process according to item (i) above, wherein the radicalreaction initiator is an azo compound.

[0026] The azo compound is preferably an azonitrile compound, anazoamidine compound, a cyclic azoamidine compound, an azoamide compound,an alkyl azo compound etc. Specific individual compounds contained inthese respective compounds include compounds known to be contained inthese compounds, but may be compounds to be found in the future.

[0027] (xi) The process according to anyone of the above items, whereinthe compound produced in the above process wherein B is a purine base ora derivative thereof, Y′ is a hydrogen atom, X′ is a hydroxyl group or aprotected hydroxyl group, is subjected to at least one step selectedfrom the step deprotecting the hydroxyl group, the step of halogenationat the 6-position, the step of amination at the 6-position and the stepof fluorination at the 2′-position to produce FddA.

[0028] (xii) A process for producing a derivative substituted with ahalogen at the 6-position, wherein the nucleic acid derivative of thegeneral formula (II) obtained above wherein B is 6-hydroxypurine ishalogenated selectively at the 6-position with a halogenating agent forexample a chlorinating agent of a combination of phosphorus oxychlorideand N,N-dimethylaniline or sulfuryl chloride and dimethylformamide or achlorinating agent such as dimethyl chloromethylene ammonium chlorideand if necessary the product is subjected to the step of deprotection,to produce the derivative halogenated at the 6-position.

[0029] (xiii) A process for producing FddA, wherein the derivativehalogenated at the 6-position obtained above is further subjected to amethod of replacing the halogen atom by an amino group (ammoniatreatment etc.) and a method of substituting the 2-position withfluorine (treatment with diethylaminosulfur trifluoride,morpholinosulfur trifluoride, or etc.) in this order or in the reverseorder and as necessary the product is subjected to the step ofdeprotection to produce FddA.

[0030] (xiv) A process for producing ddA, wherein the nucleic acidderivative of the general formula (II) obtained above wherein B isadenine and Y′ and X′ are hydrogen atoms is subjected to the step ofdeprotecting the hydroxyl group with an acid or an alkali as necessaryto produce ddA.

DETAILED DESCRIPTION OF THE INVENTION

[0031] In the nucleic acid derivatives having an eliminating group,represented by the general formula (I) and used as the starting materialin the present invention, B represents nucleic acid bases such as purinebase and pyrimidine base (including various derivatives thereof).Specifically, the pyrimidine base preferably includes uracil, thymine,cytosine etc. and the purine base preferably includes hypoxanthine,adenine, guanine etc. Further, hydroxyl groups, amino groups etc. inthese nucleic acid bases may have been protected with protecting groupsgenerally used in synthesis of nucleic acid, for example with acylgroups such as acetyl and benzoyl or aralkyl groups such as benzyl andtriphenyl methyl group. Further, as described above, the nucleic acidbases also include various derivatives thereof (e.g. derivativessubstituted with halogen atom(s)).

[0032] In the general formula (I) above, R represents a hydrogen atom ora hydroxy group-protecting group. The hydroxy group-protecting group ispreferably a protecting group which may have a substituent group(halogen atom, C₁ to C₅ alkyl group, C₁ to C₅ alkyloxy group etc.), forexample an acyl group such as acetyl or benzoyl, an alkyl group such asmethoxymethyl or allyl, an aralkyl group such as benzyl or triphenylmethyl, and a silyl group such as trimethyl silyl, and a protectingreagent therefor is preferably an acylating agent, an alkylating agent,an aralkylating agent and an organic silylating agent.

[0033] If Y is a protected hydroxyl group, R may be combined with Y toform a protecting group. Examples of protecting groups formed bycombining R with Y include cyclic protecting groups which may havesubstituent groups (halogen atom, C₁ to C₅ alkyl group, C₁ to C₅alkyloxy group etc.), preferably cyclic acetal groups and cyclic ketalgroups such as ethylidene, isopropylidene and benzylidene, cyclic silylgroups such as di-t-butylsilylene,1,1,3,3-tetraisopropyldisiloxanilidene,tetra-t-butoxydisiloxane-1,3-diylidene, etc.

[0034] One of X and Y represents an eliminating group and the otherrepresents any one of a hydrogen atom, a fluorine atom, a hydroxyl groupand a protected hydroxyl group. Here, the eliminating group representsgroups to be eliminated upon radical reaction, particularly groups oratoms to be replaced by hydrogen atoms upon radical reduction reaction,and preferable examples include halogen atoms (chlorine atom, bromineatom, iodine atom) excluding a fluorine atom, as well as O-thiocarbonylderivatives (residues) represented by the general formula (III):

[0035] In the compounds represented by the general formula (III) above,Z represents any one of H, NR′R″, OR′ and SR′, and R′ and R″ areindependent of each other and each represent any substituent group ofaryl groups (phenyl, tolyl, naphthyl etc.), alkyl groups (C₁ to C₅) oraralkyl groups (benzyl, phenethyl etc.) and alkyloxy groups (C₁ to C₅)and alkylamino groups (methylamino, ethylamino, dimethylamino etc.)which may have substituent groups (halogen atom etc.), respectively. R′and R″ may be the same or different or may be combined to form a singlecyclic group. Examples of single cyclic groups formed by theircombination include cyclic ethers (C₁ to C₅), cyclic amines (C₁ to C₅)etc.

[0036] Preferable examples of the above group Z include a hydrogen atom,methyl group, phenyl group, 1-imidazole group, N-morpholino group,methyloxy group, phenyloxy group, parafluorophenyloxy group, methylthiogroup, phenylthio group etc.

[0037] In the above general formula (I), the halogen atoms (excluding afluorine atom) in the eliminating group include e.g. a chlorine atom, abromine atom and an iodine atom.

[0038] In the compounds represented by the above general formula (I),the O-thiocarbonyl derivative in the eliminating group preferablyincludes an O-thioformyl group: H(C═S)O—, O-methylthiocarbonyl group,O-phenylthiocarbonyl group, O-(1-imidazole) thiocarbonyl group,O-(N-morpholino) thiocarbonyl group:

[0039] O-methoxythiocarbonyl group: MeO(C=S)O-, O-phenoxythiocarbonylgroup, O-parafluorophenoxythiocarbonyl group, O-methylthiothiocarbonylgroup, O-phenylthiothiocarbonyl group etc.

[0040] In the compounds of the above general formula (I), the protectedhydroxyl group represented by X or Y preferably includes acyloxy groupssuch as acetyloxy and benzoyloxy, alkyloxy groups such asmethoxymethyloxy and allyloxy, aralkyloxy groups such as benzyloxy andtriphenylmethyloxy, and silyloxy groups such as trimethylsilyloxy, andthese may have substituent groups (halogen atom, C₁ to C₅ alkyl group,C₁ to C₅ alkyloxy group etc.).

[0041] X and Y in the above general formula (I) showing the compoundsused as the starting material in the present invention may maintain thestereostructure of either α- or β-configuration, and theseconfigurations are specifically shown in the general formulae (IV) to(VII) described below. However, it is evident that the compounds whereinR is a hydrogen atom and X or Y is an eliminating group have thestereostructure of either α- or β-configuration.

[0042] In the above formulae, B represents a nucleic acid base, Rrepresents a hydrogen atom or a hydroxy group-protecting group, and oneof Y and X represents an eliminating group and the other represents ahydrogen atom, a fluorine atom, a hydroxyl group or a protected hydroxylgroup.

[0043] Further, the compounds represented by the above general formula(II) obtained by the process of the present invention are compoundswherein the eliminating group in the above general formula (I) isreduced to form a hydrogen atom, so if the other group than the reducedgroup is a fluorine group, a hydroxyl group or a protected hydroxylgroup, the compounds maintain the stereostructure at the respectivepositions and/or the stereostructure of either α- or β-configuration.Specifically, the compounds are shown in any of the following generalformulae (VIII) to (XI):

[0044] In the above formulae, B and R have the same meanings as definedabove, and one of Y′ and X′ represents a hydrogen atom and the otherrepresents a hydrogen atom, a fluorine atom, a hydroxyl group or aprotected hydroxyl group.

[0045] These nucleic acid derivatives having an eliminating grouprepresented by the above general formula (I) wherein the eliminatinggroup is a halogen atom excluding a fluorine atom can be synthesizedarbitrarily by any methods generally used for synthesis of nucleic acidderivatives (for example, see T. Ueda, “Chemistry of Nucleosides andNucleotides”, Vol. 1, L. B. Townsend, Ed., Plenum Press, New York(1988), pp. 76-79 and P. C. Srivastava, et al., “Chemistry ofNucleosides and Nucleotides”, Vol. 1, L. B. Townsend, Ed., Plenum Press,New York (1988), pp. 181-189).

[0046] For example, derivatives such as9-(2,5-di-O-acetyl-3-bromo-3-deoxy-β-D-xylofuranosyl) adenine and9-(2,5-di-0-acetyl-3-bromo-3-deoxy-p-D-xylofuranosyl) hypoxanthine canbe easily produced according to a known method (for example, seeShiragami et al., Nucleosides & Nucleotides, Vol. 15(1-3), p. 31(1996)).

[0047] As described in the literature, an acid halide (acetyl bromide,acetyl chloride etc.) is allowed to act on a nucleic acid derivativehaving a hydroxyl group whereby a desired halogen atom can be introducedinto it.

[0048] In addition, these nucleic acid derivatives having an eliminatinggroup represented by the above general formula (I) wherein theeliminating group is an O-thiocarbonyl derivative (residue) can bearbitrarily synthesized by introducing a thiocarbonyl group to thecorresponding nucleic acid derivatives having a hydroxyl group. Thecorresponding nucleic acid derivatives having a hydroxyl group can bearbitrarily synthesized by any methods generally used for synthesis ofnucleic acid derivatives (for example, the method described in“Chemistry of Nucleosides and Nucleotides”, L. B. Townsend, Ed., PlenumPress, New York (1988)).

[0049] To introduce the thiocarbonyl group, a generally used method (forexample, see S. W. McCombie “Comprehensive Organic Synthesis”, Vol. 8,B. M. Trost, Ed., Pergamon Press (1991), pp. 818-824) can be used. Thedesired compounds can be obtained by allowing the corresponding nucleicacid derivatives having a hydroxyl group to react with thiocarbonylhalides represented by the general formula (XII) below or to react withcarbon disulfide and alkyl halides corresponding to R′ when Z is SR′

[0050] In the above formula, Z represents any one of H, NR′R″, OR′ andSR′, and R′ and R″ may be independent of each other and each representany substituent group of an aryl, alkyl or aralkyl group and alkyloxyand alkylamino groups which may have a substituent group (halogen atometc.), respectively. R′ and R″ may be the same or different or may becombined to form a single cyclic group. Examples of single cyclic groupsformed by their combination include cyclic ethers (C₁ to C₅), cyclicamines (C₁ to C₅) etc., and specific examples include an imidazolegroup, a morpholino group etc. “A” represents a halogen atom.

[0051] The reaction of introducing the thiocarbonyl group may beconducted in the presence of an equivalent-range base. The reaction maybe conducted in a suitable solvent, and preferably, the suitable solventincludes organic solvents such as ethyl acetate, toluene, methylenechloride, acetonitrile and a mixed solvent thereof. The reaction in thiscase can be conducted at −80° C. to the reflux temperature of thesolvent. After the reaction, the base is neutralized if necessary andthe reaction mixture is subjected in a usual manner to extraction withan organic solvent such as ethyl acetate, toluene and methylene chloridewhereby the thiocarbonyl derivative can be isolated. After the reaction,the reaction mixture can be used directly in radical reduction reactionwithout isolating the thiocarbonyl derivative.

[0052] In the present invention, any one of hypophosphorous acid, saltsof hypophosphorous acid and esters of phosphorous acid is used as aradical reducing agent. Preferable examples of salts of hypophosphorousacid include alkali metal salts such as sodium hypophosphite, alkalineearth metal salts such as calcium hypophosphite, amine salts such asammonium hypophosphite, and metal salts such as nickel hypophosphite(II).

[0053] Preferable examples of such esters of phosphorous acid includelower alcohol (C₁ to C₅) phosphorous acid ester (mono-, di-ester), suchas dimethyl phosphite, diethyl phosphite etc.

[0054] The radical reaction initiator used in the present invention maybe any of those known as radical reaction initiators and radicalreaction reagents, and such radical reaction initiators may bepreferably azo compounds. Preferable examples of azo compounds includeazonitrile compounds such as azobisisobutyronitrile, azoamidinecompounds such as 2,2′-azobis(2-methylpropionamidine) dihydrochloride(trade name: V-50), cyclic azoamidine compounds such as 2,2′-azobis[2-(2-imidazoline-2-yl) propane] dihydrochloride (trade name: VA-044),2,2′-azobis[2-(2-imidazoline-2-yl) propane] disulfate (trade name:VA-044B) and 2,2′-azobis[2-(2-imidazoline-2-yl) propane] (trade name:VA-061), azoamide compounds such as2,2′-azobis[2-methyl-N-(2-hydroxyethyl) propionamide] (trade name:VA-086), and alkyl azo compounds such as azodi-t-octane (trade name:VR-110).

[0055] The radical reduction reaction can be conducted using anequivalent to excess radical reaction reagent in a solvent preferablywater, but may be conducted in an organic solvent such as ethyl acetate,toluene, methylene chloride and acetonitrile (or a mixture of thesesolvents). The reaction may also be conducted in an arbitrary mixture ofwater and one or more of these organic solvents as the solvent. Thereaction may be conducted at room temperature to the reflux temperatureof the solvent. An equivalent or more radical reaction initiator can beused, but usually a catalytic amount (0.1 to 100 mol-%) suffices. Afterthe reaction, the product is isolated by extracting the reaction mixturewith an organic solvent such as ethyl acetate, toluene or methylenechloride in a usual manner, or by merely filtering its formed crystals.

[0056] Out of the compounds of the above general formula (II) obtainedin the manner as described above, the compound wherein B is adenine, Y′is a hydrogen atom, X′ is a hydrogen atom or a fluorine atom in theβ-configuration and R is a hydrogen atom, is used as a pharmaceuticalpreparation or it is an expected compound 2′,3′-dideoxyadenosine (ddA)or 9-(2,3-dideoxy-2-fluoro-β-D-threo-pentofuranosyl) adenine (FddA), orthe product wherein R is not a hydrogen atom but a protecting group canbe subjected to a deprotection step to be easily converted into theabove ddA or FddA. In this case, the protecting group R for the hydroxylgroup at the 5′-position is eliminated in a usual manner with acid oralkali as necessary whereby the objective compound can be produced.

[0057] For example, if the protecting group R for the hydroxyl group atthe 5′-position is a trityl group which may have a substituent group,the compounds are treated with an acid such as acetic acid so that theycan be deprotected.

[0058] In the above, the compounds wherein B is not adenine but6-halogenopurine are subjected in a usual manner to the step ofamination at the 6-position whereby an amino group is introduced intothe 6-position thereof, and in the case of those wherein R is not ahydrogen atom but a hydroxy group-protecting group, the objectiveprotecting group is similarly eliminated (deprotected) before or afterthe step of amination at the 6-position whereby ddA or FddA can beproduced. If X′ is neither a hydrogen atom nor a fluorine atom at theβ-configuration but a hydroxyl group (protected or not protected), thehydroxyl group is dehydroxylated in a usual manner, or dehydroxylatedand fluorinated at the β-position, whereby ddA or FddA can be produced.In this case, the step of dehydroxylating the hydroxyl group or the stepof dehydroxylation-fluorination at the i-position can be conducted usingany methods known in the art.

[0059] If B is not adenine (if B is adenine, ddA and FddA can beproduced by the step of dehydroxylation or dehydroxylation-fluorinationat the β-position and subsequent deprotection of R as necessary when Ris a protecting group) but 6-halogenopurine, then the dehydroxylationstep or the dehydroxylation-fluorination at the β-position can also beconducted before the step of amination at the 6-position.

[0060] Similarly, the compound (II) produced in the present inventionwherein B is 6-hydroxypurine, Y′ is a hydrogen atom and X′ is a hydroxylgroup or a protected hydroxyl group is subjected to the step ofhalogenation at the 6-position to produce the compound substituted witha halogen at the 6-position, which is then subjected to the step offluorination at the 2′-1-position and the step of amination at the6-position, and if R is aprotecting group, the compound is furthersubjected to the step of deprotection whereby FddA can be produced.

[0061] However, the order of the step of fluorination at the 2′-positionand the step of amination at the 6-position is particularly not limited.Further, if the compound has a protected hydroxyl group, the protectinggroup may be eliminated, and then the compound may be subjected to thestep of halogenation at the 6-position, and if the halogen-substitutedcompound has a protected hydroxyl group, the protecting group for thehydroxyl group may be eliminated, and then the compound may be subjectedto the step of amination at the 6-position.

[0062] That is, in the case of the derivative wherein Y′ is a hydrogenatom and B is 6-hydroxypurine, an amino group is introduced into thisderivative if necessary via the step of halogenation at the 6-position,while in the case of the derivative wherein X′ is neither a hydrogenatom nor a fluorine atom but a hydroxyl group (protected or notprotected), the derivative is subjected as necessary to the step ofdehydroxylation, or the step of dehydroxylation-fluorination at theβ-position, for the hydroxyl group (X′), whereby ddA, FddA and theirrelated compounds can be produced. The order for conducting these stepsis not particularly limited to the order described and can be suitablyselected.

[0063] Now, whole contents of Japanese Application No. 311918/1998,based on which the priority is claimed for this application, isincorporated by references in the specification of this application, ifnecessary.

EXAMPLES

[0064] Hereinafter, the present invention is described in more detail byreference to the Reference Examples and Examples.

Reference Example 1

[0065] Synthesis of5′-O-trityl-3′-O-phenoxythiocarbonyl-2′-deoxy-adenosine from5′-O-trityl-2′-deoxy-adenosine

[0066] 0.50 g of 5′-O-trityl-2′-deoxy-adenosine was dissolved in 10.1 mldry acetonitrile, and 373.9 mg (3 equivalents) of DMAP was addedthereto. This solution was cooled to 0° C., and 0.28 ml (2 equivalents)of phenoxythiocarbonyl chloride was added slowly. This reaction solutionwas raised to room temperature and stirred as such for 3 hours, and 62.3mg DMAP and 70.0 μl phenoxythiocarbonyl chloride were further addedthereto. This reaction solution was stirred at room temperature for 2days, and then 1.0 ml methanol was added to stop the reaction. Thisreaction solution was stirred for 30 minutes, and 30 ml methylenechloride and 15 ml aqueous saturated sodium hydrogen carbonate wereadded thereto, and the mixture was stirred vigorously. The separatedorganic layer was washed with 10 ml saturated saline, dried over sodiumsulfate and concentrated. The resulting oily residue was purified withsilica gel column chromatography (eluent: hexane/ethyl acetate) whereby144.1 mg of the object compound (yield: 17.9%) was obtained.

Example 1

[0067] Synthesis of 5′-O-trityl-2′,3′-dideoxy-adenosine from5′-O-trityl-3′-O-phenoxythiocarbonyl-2′-deoxy-adenosine

[0068] 144.1 mg of5′-O-trityl-3′-O-phenoxythiocarbonyl-2′-deoxy-adenosine was dissolved in2.29 ml dimethoxyethane, and 0.18 ml triethylamine (5.5 equivalents) and0.12 ml of 50% aqueous hypophosphorous acid (H₃PO₂; 5.0 equivalents)were added thereto. 1.0 mg of 2,2′-azobisisobutyronitrile (AIBN) wasadded to this solution and heated under reflux at 90° C. for 1 hour, andfurther 1.0 mgAIBN was added thereto, and the mixture was heated underreflux at 90° C. for 1 hour. This reaction solution was left at roomtemperature overnight, and further 3.0 mg AIBN was added thereto, andthe mixture was heated under reflux at 90° C. for 6 hours. When thereaction was confirmed by high performance liquid chromatography (HPLC),it was found that the objective compound was formed in an area ratio of2%.

Reference Example 2

[0069] Synthesis of5′-O-trityl-3′-o-methylthiothiocarbonyl-2′-deoxy-adenosine from5′-o-trityl-2′-deoxy-adenosine

[0070] 1.0 g of 5′-O-trityl-2′-deoxy-adenosine was dissolved in 4.0 mlDMSO, and 0.24 ml (2 equivalents) of carbon disulfide was added thereto.This solution was cooled to 15° C., and 0.45 ml (1.1 equivalents) of 5 Naqueous sodium hydroxide was added slowly. This reaction solution wasstirred at 15° C. for 30 minutes, and 0.14 ml (1.1 equivalents) ofmethyl iodide was added slowly. This reaction solution was stirred at15° C. for 1.5 hours and added dropwise to 35 ml separately preparedwater to stop the reaction. This reaction solution was stirred at roomtemperature for 20 minutes, and the resulting crystals were filtered andwashed with 15 ml water and 20 ml hexane. The crystals were air-driedovernight and dried at 40° C. under reduced pressure to give 1.14 g(yield: 96.4%) of the title objective compound.

Example 2

[0071] Synthesis of 5′-O-trityl-2′,3′-dideoxy-adenosine from5′-O-trityl-3′-O-methylthiothiocarbonyl-2′-deoxy-adenosine

[0072] 1.14 g of5′-O-trityl-3′-O-methylthiothiocarbonyl-2′-deoxy-adenosine was dissolvedin 5.0 ml dimethoxyethane, and 2.85 ml triethylamine (10 equivalents)and 1.05 ml of 50% aqueous hypophosphorous acid (5 equivalents) wereadded thereto. This solution was heated to 70° C., and 66.5 mg (0.2equivalent) of AIBN dissolved in 4.0 ml dimethoxyethane was addedthereto. After 1.5 hours, 33.3 mg (0.1 equivalent) of AIBN was furtheradded thereto and heated under reflux for 1 hour. This reaction solutionwas cooled to room temperature and added dropwise to a separatelyprepared mixture of 50 ml methylene chloride and 30 ml saturated salineto stop the reaction. The organic layer was separated, dried overmagnesium sulfate and concentrated. The resulting oily residue wasrecrystallized from toluene and the first crystals and the secondcrystals were combined to give the title objective compound in 56.1%yield.

Reference Example 3

[0073] Synthesis of6-chloro-9-(5-O-trityl-3-O-benzoyl-2-deoxy-2-fluoro-β-D-arabinofuranosyl)-9H-purine

[0074] 5′-o-trityl-3′-O-benzoyl-6-chlorpurine riboside (4.76 g, 7.5mmol) was dissolved in 100 ml dry methylene chloride, and 3.6 ml (44.5mmol) of pyridine was added thereto. After the mixture was cooled onice, diethylaminosulfur trifluoride (DAST, 2.25 ml, 17 mmol) was addeddropwise thereto under stirring, allowed to reach room temperature andfurther heated under reflux for 5 hours. After cooling, the reactionsolution was added dropwise to 500 ml of 5% aqueous sodium hydrogencarbonate under vigorous stirring and stirred for 20 minutes. It wastransferred to a separating funnel and shaken well, and the organiclayer was recovered. The aqueous layer was washed with 100 mlchloroform. The organic layers were combined, washed with 200 ml water,dried over magnesium sulfate and filtered, and the solvent was distilledoff. The residues were subjected to azeotropic distillation with tolueneuntil the smell of pyridine disappeared, and then the reaction solutionwas dissolved in 50 ml benzene, subjected to a silica gel column (3.5×50cm) and eluted with 0 to 12.5% ethyl acetate/benzene solution (4000 ml).Product fractions were collected and the solvent was distilled offwhereby caramel was obtained. Yield, 3.80 g (FW: 635.1, 5.99 mmol, 80%).

[0075]¹H-NMR (CDCl₃) δ: 8.76 (1H, s, H2), 8.36 (H, d, J=3.0 Hz, H8),7.2-8.1 (ca 20H, Bz, Tr), 6.66 (1H, dd, J=21.7, J=2.7 Hz, H1′), 5.70(1H, dd, J=17.0, J=3.0 Hz, H3′), 5.28 (1H, ddd, J=50.0, J=3.0, J=0.8 Hz,H2′), 4.42 (1H, m, H4′), 3.62 (1H, dd, J=10.4, J=5.2 Hz, H1a), 3.54 (1H,dd, J=10.4, J=4.1 Hz, H5′ b)

[0076] Synthesis of 9-(5-O-trityl-2-deoxy-2-fluoro-β-D-arabinofuranosyl)Adenine

[0077]6-Chloro-9-(5-O-trityl-3-O-benzoyl-2-deoxy-2-fluoro-β-D-arabinofuranosyl)-9-H-purine(3.15 g, 4.98 mmol) was dissolved in 100 ml methanolic ammonia(saturated at 0° C.) and left in a sealed tube at 100° C. for 2 days.After cooling, the solvent was carefully distilled off, and the residueswere dissolved in 100 ml chloroform. The insolubles were filtered offand the solution was applied to a silica gel column (3.5×50 cm) andeluted with 3 to 10% ethanol/methylene chloride solution (4000 ml).Product fractions were collected, and the solution was concentrated togive white crystals (1.87 g, 3.66 mmol, 73%).

[0078] Melting point: 210.5-212.5° C.

[0079] Synthesis of9-(5-O-trityl-3-O-methylthiothiocarbonyl-2-deoxy-2-fluoro-o-D-arabinofuranosyl)adenine from 9-(5-O-trityl-2-deoxy-2-fluoro-o-D-arabinofuranosyl)Adenine

[0080] 246.3 mg (purity: 95.2%) of9-(5-O-trityl-2-deoxy-2-fluoro-β-D-arabinofuranosyl) adenine wasdissolved in 0.91 ml DMSO, and 0.055 ml (2 equivalents) of carbondisulfide was added thereto. This solution was cooled to 15° C., and 0.1ml (1.1 equivalents) of 5 N aqueous sodium hydroxide was added slowly.This reaction solution was stirred at 15° C. for 30 minutes, and 0.032ml (1.1 equivalents) of methyl iodide was added slowly. This reactionsolution was stirred at 15° C. for 1.3 hours, and further 0.03 ml carbondisulfide and 0.1 ml of 5 N aqueous sodium hydroxide were added slowly.This reaction solution was stirred at 15° C. for 30 minutes, and 0.03 mlmethyl iodide was added slowly. This reaction solution was stirred at15° C. and added dropwise to 10 ml separately prepared water to stop thereaction. The resulting crystals were filtered, and the crystals werewashed twice with 10 ml water and 10 ml hexane. The crystals were driedunder reduced pressure at room temperature to give 250.9 mg (purity,66.8%; yield, 60.8%) of the objective compound.

Example 3

[0081] Synthesis of9-(2,3-dideoxy-2-fluoro-5-O-triy-β-D-threo-pentofuranosyl) Adenine from9-(5-O-trityl-3-O-methylthiothiocarbonyl-2-deoxy-2-fluoro-β-D-arabinofuranosyl)Adenine

[0082] 200 mg of9-(5-O-trityl-3-O-methylthiothiocarbonyl-2-deoxy-2-fluoro-β-D-arabinofuranosyl)adenine was dissolved in 0.73 ml dimethoxyethane, and 0.42 mltriethylamine (13.6 equivalents) and 0.16 ml of 50% aqueoushypophosphorous acid (7 equivalents) were added thereto. This solutionwas heated until reflux, and 14.7 mg (0.4 equivalent) of AIBN dissolvedin 0.44 ml dimethoxyethane was added thereto. After 5 hours, 14.7 mg(0.4 equivalent) of AIBN dissolved in 0.44 ml dimethoxyethane wasfurther added thereto and heated under reflux 20 minutes. This reactionsolution was cooled to room temperature, followed by adding 3 mlmethylene chloride and 3 ml water dropwise to stop the reaction. Theorganic layer was separated and concentrated to give a solid substancewhich was then recrystallized from 3 ml toluene. The crystals were driedunder reduced pressure to give the title objective compound in 70.2%.

Reference Example 4

[0083] Synthesis of9-(5-O-trityl-3-O-methylthiothiocarbonyl-2-deoxy-2-fluoro-p-D-arabinofuranosyl)adenine from 9-(5-O-trityl-2-deoxy-2-fluoro-β-D-arabinofuranosyl)adenine 174.0 mg (purity: 86.5%) of9-(5-O-trityl-2-deoxy-2-fluoro-β-D-arabinofuranosyl) adenine wasdissolved in 1.2 ml DMSO and cooled to 13° C. 0.065 ml (1.1 equivalents)of 5 N aqueous sodium hydroxide and 0.072 ml (4 equivalents) of carbondisulfide were added thereto. This reaction solution was stirred at 13°C. for 15 minutes, and 0.036 ml (2 equivalents) of methyl iodide wasadded thereto. This reaction solution was added dropwise to 10 mlseparately prepared water to stop the reaction. The resulting crystalswere filtered, and the crystals were recrystallized from 3 mlacetonitrile and 4 ml water. The crystals were filtered, washed withwater and dried at 45° C. under reduced pressure to give 127.9 mg(yield, 72.2%) of the title objective compound.

[0084] Synthesis of9-(5-O-trityl-3-O-methylthiothiocarbonyl-2-deoxy-2-fluoro-β-D-arabinofuranosyl)adenine from 9-(5-O-trityl-2-deoxy-2-fluoro-β-D-arabinofuranosyl)Adenine

[0085] 4.80 g (purity: 86.5%) of9-(5-O-trityl-2-deoxy-2-fluoro-β-D-arabinofuranosyl) adenine wasdissolved in 33 ml DMSO and cooled to 12° C. 1.79 ml (1.1 equivalents)of 5 N aqueous sodium hydroxide and 1.94 ml (4 equivalents) of carbondisulfide were added slowly to this solution. Further, 1.01 ml (2equivalents) of methyl iodide was further added slowly to this reactionsolution. This reaction solution was stirred at 12° C. for 30 minutesand added dropwise to a separately prepared mixture of 50 ml water and50 ml ethyl acetate to stop the reaction. The organic layer wasseparated and washed with 50 ml water, and this organic layer wasconcentrated to give an oily residue. This oily residue wasrecrystallized from 20 ml acetonitrile and filtered, and the crystalswere dried at 45° C. under reduced pressure to give 3.95 g (purity,98.0%; yield, 79.3%) of the objective compound.

Example 4

[0086] Synthesis of9-(2.3-dideoxy-2-fluoro-5-O-tri-β-D-threo-pentofuranosyl) adenine from9-(5-O-trityl-3-O-methylthiothiocarbonyl-2-deoxy-2-fluoro-β-D-arabinofuranosyl)Adenine—No. 2

[0087] 102.13 mg of9-(5-O-trityl-3-O-methylthiothiocarbonyl-2-deoxy-2-fluoro-β-D-arabinofuranosyl)adenine (purity: 98.0%) was dissolved in 0.83 ml dimethoxyethane, and0.46 ml triethylamine (20 equivalents) and 0.172 ml of 50% aqueoushypophosphorous acid (10 equivalents) were added thereto. This solutionwas heated until reflux, and 16.4 mg (0.6 equivalent) of AIBN dissolvedin 0.49 ml dimethoxyethane was added in 3 portions. This reactionsolution was heated under reflux for 1 hour and 45 minutes and thencooled to room temperature, followed by adding 5 ml methylene chlorideand 5 ml water dropwise to stop the reaction. The organic layer wasseparated and concentrated to give a solid substance which was thenrecrystallized from a mixture of 3.2 ml toluene and 3.2 ml methanol. Thecrystals were dried under reduced pressure to give the objectivecompound in 86.1%.

Example 5

[0088] Synthesis of 2′,5′-di-O-acetyl-3′-deoxy-inosine from9-(2,5-di-O-acetyl-3-bromo-3-deoxy-P-D-xylofuranosyl) Hypoxanthine

[0089] 14.4 ml acetonitrile and 7.2 ml water were added to the solutionof 24.98 g acetonitrile and 10.01 g of9-(2,5-di-O-acetyl-3-bromo-3-deoxy-p-D-xylofuranosyl) hypoxanthinedissolved therein. A solution previously prepared by mixing 10.7 gtriethylamine (4.4 equivalents) with 12.7 g of 50% aqueoushypophosphorous acid (4.0 equivalents) was added thereto. The pH valueof this solution was decreased from 8.7 to 7.0 by adding 5 drops of 50%aqueous hypophosphorous acid. This solution was heated to 70° C., and395.4 mg (0.1 equivalent) of AIBN dissolved in 3.0 ml acetonitrile wasadded thereto. This reaction solution was heated under reflux for 1hour, then cooled to room temperature and neutralized to pH 7.0 with 25%aqueous sodium hydroxide. This reaction solution was concentrated, and70 ml water was added to the residues which were then stirred at 60° C.for 1 hour and cooled to room temperature. The formed crystals werefiltered and the crystals were washed with 25 ml water and 10 mlethanol. The crystals were dried at 50° C. under reduced pressure togive 5.93 g (purity, 85.1%; yield, 62.2%) of the title object compound.

Example 6

[0090] Synthesis of 2′,5′-di-O-acetyl-3′-deoxy-inosine from9-(2.5-di-O-acetyl-3-bromo-3-deoxy-β-D-xylofuranosyl) Hypoxanthine—No. 2

[0091] A solution previously prepared by dissolving 10.44 g sodiumhypophosphite monohydrate (4.0 equivalents) in 11.2 ml water was addedto the solution obtained by dissolving 10.23 g of9-(2,5-di-O-acetyl-3-bromo-3-deoxy-β-D-xylofuranosyl) hypoxanthine in37.24 g acetonitrile.

[0092] 4 N aqueous sodium hydroxide was added to this solution wherebythe pH value was raised from 5.8 to 7.0. This solution was heated to 70°C., and 404.6 mg (0.1 equivalent) of AIBN dissolved in 3.0 mlacetonitrile was added thereto. This reaction solution was stirred at70° C. for 2 hours, then cooled to room temperature and neutralized topH 7.0 with 4 N aqueous sodium hydroxide. This reaction solution wasconcentrated, and 50 ml water was added to the residues, stirred at 60°C. for 1 hour and then cooled to room temperature. The resultingcrystals were filtered and the crystals were dried at 40° C. underreduced pressure whereby 4.89 g (purity, 82.6%; yield, 48.8%) of thetitle objective compound was obtained.

Example 7

[0093] Synthesis of 2′,5′-di-O-acetyl-3′-deoxy-inosine from9-(2.5-di-O-acetyl-3-bromo-3-deoxy-β-D-xylofuranosyl) Hypoxanthine—No. 3

[0094] 9.74 ml of 50% aqueous hypophosphorous acid (3.0 equivalents) wasadded to 63 ml water and cooled to 10° C., and 12.5 ml triethylamine(3.0 equivalents) was added thereto. The resulting solution was added tothe solution of 31.38 g acetonitrile and 2.46 g of9-(2,5-di-O-acetyl-3-bromo-3-deoxy-β-D-xylofuranosyl) hypoxanthinedissolved therein. 3.4 ml triethylamine was added to this solutionwhereby the pH value was raised from 4.3 to 8.0. This solution washeated to 60° C., and 811.7 mg (0.1 equivalent) of V-50[2,2′-azobis(2-methylpropionamidine) dihydrochloride] dissolved in 5.0ml water was added thereto. This reaction solution was stirred at 60° C.for 1 hour, neutralized to pH 4.5 with 4.0 ml of 25% aqueous sodiumhydroxide, further stirred at 60° C. for 1 hour and then cooled to roomtemperature. The resulting crystals were filtered and the crystals werewashed with 35 ml water. The crystals were dried at 55° C. under reducedpressure whereby 5.54 g (purity, 56.3%; yield, 54.9%) of the titleobjective compound was obtained.

Example 8

[0095] Synthesis of 2′,5′-di-O-acetyl-3′-deoxy-inosine from9-(2,5-di-O-acetyl-3-bromo-3-deoxy-β-D-xylofuranosyl) Hypoxanthine—No. 4

[0096] A solution previously prepared by dissolving 15.43 g sodiumhypophosphite monohydrate (2.0 equivalents) in 111 ml water was added tothe solution of 74.03 g of acetonitrile and 30.06 g of9-(2,5-di-O-acetyl-3-bromo-3-deoxy-β-D-xylofuranosyl) hypoxanthinedissolved therein. 25% aqueous sodium hydroxide was added to thissolution to adjust the pH value to 8.5. This solution was heated to 55°C., and 1.96 g (0.1 equivalent) of V-50 [2,2′-azobis(2-methylpropionamidine) dihydrochloride]was added thereto. After thisreaction solution was stirred at 60° C. for 1 hour, 111 ml water wasadded thereto, and the solution was further stirred at 60° C. for 1hour. This reaction solution was neutralized to pH 7.0 with 25% aqueoussodium hydroxide. This reaction solution was further stirred at 60° C.for 1 hour, then cooled to 5° C. and stored overnight, followed byraising the temperature to 22° C. and stirring for 4 hours. Theresulting crystals were filtered and the crystals were washed with 26 mlwater and 10 ml ethanol. The crystals were dried at 55° C. under reducedpressure whereby the title objective compound was obtained with 72.8%purity in 50.0% yield.

Example 9

[0097] Synthesis of 2′,5′-di-O-acetyl-3′-deoxy-inosine from9-(2,5-di-o-acetyl-3-bromo-3-deoxy-β-D-xylofuranosyl) Hypoxanthine—No. 5

[0098] 19.8 g of 50% aqueous hypophosphorous acid (3.0 equivalents) wasadded to 104 ml water and cooled to 16° C., and 15.23 g triethylamine(3.0 equivalents) was added thereto. The resulting solution was added tothe solution of 51.18 g acetonitrile and 20.76 g of9-(2,5-di-O-acetyl-3-bromo-3-deoxy-β-D-xylofuranosyl) hypoxanthinedissolved therein. The temperature of this solution was raised to 43°C., and triethylamine was added to raise the pH value from 3.8 to 8.0.This solution was heated to 49° C., and 1.62 g (0.1 equivalent) ofVA-044 [2,2′-azobis[2-(2-imidazoline-2-yl) propane] dihydrochloride]dissolved in 8.3 ml water was added thereto. This reaction solution wasstirred at 50° C. for 30 minutes, neutralized to pH 4.0 with 3.54 g of25% aqueous sodium hydroxide, further stirred at 50° C. for 1.5 hoursand cooled to 10° C. This reaction solution was neutralized to pH 6.0with 5.94 g of 25% aqueous sodium hydroxide. This reaction solution wasstirred at 10° C. for 1.5 hours, and the resulting crystals werefiltered and washed with 62 ml water. The title objective compound wasobtained in 80.6% yield as determined by analysis of the crystals.

Example 10

[0099] Synthesis of 2′,5′-di-O-acetyl-3′-deoxy-inosine from9-(2.5-di-O-acetyl-3-bromo-3-deoxy-β-D-xylofuranosyl) Hypoxanthine—No. 6

[0100] A solution previously prepared by dissolving 3.716 g sodiumhypophosphite monohydrate (NaH₂PO₂.H₂O; 2.0 equivalents) in 33.4 mlwater was added to the solution of 18.16 g acetonitrile and 7.21 g of9-(2,5-di-O-acetyl-3-bromo-3-deoxy-β-D-xylofuranosyl) hypoxanthinedissolved therein. 1.8 ml of 25% aqueous sodium hydroxide was added tothis solution to adjust the pH value to 8.5. This solution was heated to60° C., and 560.8 mg (0.1 equivalent) of VA-044[2,2′-azobis[2-(2-imidazoline-2-yl) propane] dihydrochloride] dissolvedin 2.8 ml water was added thereto. While this reaction solution was keptat pH 4.0 by suitably adding 25% aqueous sodium hydroxide, the solutionwas stirred at 60° C. for 1 hour. This reaction solution was cooled toroom temperature and neutralized to pH 6.2 with 25% aqueous sodiumhydroxide. The resulting crystals were filtered and the crystals werewashed with 17.6 ml water and 2 ml ethanol. The crystals were dried at60° C. under reduced pressure whereby 5.089 g (purity:77.6%;yield:67.6%) of the title objective compound was obtained.

Example 11

[0101] Synthesis of 2′,5′-di-O-acetyl-3′-deoxy-inosine from9-(2.5-di-O-acetyl-3-bromo-3-deoxy-p-D-xylofuranosyl) Hypoxanthine—No. 7

[0102] A solution previously prepared by dissolving 1.06 g sodiumhypophosphite monohydrate (2.0 equivalents) in 9.47 ml water was addedto the solution of 11.27 g acetonitrile and 2.03 g of9-(2,5-di-β-acetyl-3-bromo-3-deoxy-p-D-xylofuranosyl) hypoxanthinedissolved therein. 0.76 g of 25% aqueous sodium hydroxide was added tothis solution and further 0.14 g (0.1 equivalent) of VA-086[2,2′-azobis[2-methyl-N-(2-hydroxyethyl) propionamide]] dissolved in 1.4ml water was added thereto. 0.12 g of 6 N hydrochloric acid was added tothis reaction solution to adjust the pH value to 8.6. This reactionsolution was stirred at 60° C. overnight and further stirred at 68° C.for 2 hours whereby the title objective compound was obtained in 1.2%yield as determined by HPLC analysis.

Example 12

[0103] Synthesis of 2′,5′-di-O-acetyl-3′-deoxy-inosine from9-(2,5-di-O-acetyl-3-bromo-3-deoxy-β-D-xylofuranosyl) Hypoxanthine—No. 8

[0104] A solution previously prepared by dissolving 3. 18 g sodiumhypophosphite monohydrate (2.0 equivalents) in 28.6 ml water was addedto the solution of 15.34 g acetonitrile and 6.23 g of9-(2,5-di-O-acetyl-3-bromo-3-deoxy-β-D-xylofuranosyl) hypoxanthinedissolved therein. 1.49 g of 25% aqueous sodium hydroxide was added tothis solution to adjust the pH value to 8.5. 0.58 g (0.1 equivalent) ofVA-044B [2,2′-azobis[2-(2-imidazoline-2-yl) propane] disulfate]dissolved in 3.0 ml water was added to this solution. This reactionsolution was adjusted to pH 8.5 by adding 0.59 g of 25% aqueous sodiumhydroxide, and the reaction solution was stirred at 60° C. for 1 hour.This reaction solution was neutralized to pH 7.0 by adding 5.75 g of 25%aqueous sodium hydroxide and then cooled to room temperature. Theresulting crystals were filtered and the crystals were washed with 16.5ml water. The crystals were dried at 60° C. under reduced pressurewhereby 3.87 g (purity, 58.1%; yield, 44.6%) of the title objectivecompound was obtained.

Reference Example 5

[0105] Synthesis of(−)-3′-5′-O-(1,1,3,3-tetraisopropyl-1.3-disiloxanediyl)-2′-O-imidazolylthiocarbonyl-adenosinefrom (−)-3′,5′-O-(1,1,3,3-tetraisopropyl-1.3-disiloxanediyl) adenosine

[0106] 0.76 g of (−)-3′,5′-O-(1,1,3,3-tetraisopropyl-1,3-disiloxanediyl)adenosine was dissolved in 15 ml dry dimethylformamide, and 0.74 g of1,1′-thiocarbonyldiimidazole was added thereto. This reaction solutionwas stirred at room temperature overnight, followed by raising thetemperature to 70° C. and stirring for 6 hours. 250 ml ethyl acetate and50 ml water were added to this reaction solution to stop the reaction.The organic layer was separated, washed twice with 50 ml water, thendried over magnesium sulfate and concentrated. The resulting oilyresidue was purified by silica gel column chromatography (eluent:methanol/methylene chloride) to give 0.76 g (purity: 81.7%) of theobjective compound.

Example 13

[0107] Synthesis of 2′-deoxyadenosine from(−)-3′,5′-O-(1,1,3,3-tetraisopropyl-1.3-disiloxanediyl)-2′-O-imidazolylthiocarbonyl-adenosine

[0108] 692 mg of(−)-3′,5′-O-(1,1,3,3-tetraisopropyl-1,3-disiloxanediyl)-2′-O-imidazolylthiocarbonyl-adenosinewas dissolved in 4.6 ml dimethoxyethane and added to 0.86 mltriethylamine (5.5 equivalents) and 0.60 ml of 50% aqueoushypophosphorous acid (5.0 equivalents). After 18.3 mgAIBN was added tothis solution, the mixture was heated under reflux at 100° C. for 30minutes, and after 18.3 mg AIBN was further added to this solution, themixture was heated under reflux at 100° C. for 30 minutes. This reactionsolution was cooled to room temperature, and 20 ml ethyl acetate, 10 mldimethoxy ethane and 10 ml water were added to stop the reaction. Theorganic layer was separated and concentrated to give an oily residue.This oily residue was dissolved in 5.0 ml tetrahydrofuran, and 2.0 ml of1.0 M tetrabutyl ammonium fluoride in tetrahydrofuran was added thereto.This solution was stirred at 70° C. for 1 hour and cooled to roomtemperature. This reaction mixture was concentrated, and 30 ml water and20 ml diethyl ether were added thereto, and the aqueous layer was washedtwice with 20 ml diethyl ether. The title objective compound wasobtained in 33% yield as determined by HPLC analysis.

Example 14

[0109] Synthesis of9-(2,3-dideoxy-2-fluoro-5-O-trityl-β-D-threopentofuranosyl) adenine from9-(5-O-trityl-3-O-methylthiothiocarbonyl-2-deoxy-2-fluoro-β-D-arabinofuranosyl)Adenine—No. 3

[0110] 60.2 mg of9-(5-O-trityl-3-O-methylthiothiocarbonyl-2-deoxy-2-fluoro-β-D-arabinofuranosyl)adenine (purity: 98.0%) was dissolved in 1.0 ml dimethoxyethane, and 110mg of dimethyl phosphite ((CH₃O)₂P(O)H; 10 equivalents) was addedthereto. This solution was heated until reflux, and 10.0 mg (0.6equivalent) of AIBN dissolved in 0.6 ml dimethoxyethane was added in 3portions.

[0111] This reaction solution was heated under reflux for 2 hours andthen cooled to room temperature. The solution was concentrated underreduced pressure to give the objective compound in yield 84.1% asdetermined by HPLC analysis.

[0112] The reaction was conducted in the same manner as above in Example14, except using 138 mg of diethyl phosphite (10 equivalents) in placeof the 110 mg of dimethyl phosphite (10 equivalents). Thus obtainedreaction solution was cooled to room temperature, and the solution wasconcentrated under reduced pressure to give the objective compound inyield 82.2% as determined by HPLC analysis.

[0113] Effects of the Invention

[0114] According to the present invention, sugar-moiety hydroxyl groupsand halogen atoms in nucleic acid derivatives (including nucleic acidsor derivatives thereof and nucleic acid-related compounds) can beradically reduced with any one of hypophosphorous acids which may be inthe salts thereof, and phosphites (esters), so this process can beutilized to provide an industrially useful and highly safe process forproducing the reduced compounds at low costs.

What is claimed is:
 1. A process for producing a nucleic acidderivatives represented by the general formula (II):

wherein B represents a nucleic acid base which may be in the form ofderivative thereof, R represents a hydrogen atom or a hydroxygroup-protecting group, and one of Y′ and X′ represents a hydrogen atomand the other represents a hydrogen atom, a fluorine atom, a hydroxylgroup or a protected hydroxyl group, respectively, which comprisesallowing a nucleic acid derivative having an eliminating grouprepresented by the general formula (I):

wherein B and R have the same meanings as defined above, and one of Yand X represents an eliminating group and the other represents ahydrogen atom, a fluorine atom, a hydroxyl group or a protected hydroxylgroup, respectively, to react with at least one compound selected fromhypophosphorous acids, which may or may not be in the salts thereof, andesters of phosphorous acid in the presence of a radical reactioninitiator.
 2. The process according to claim 1, wherein B is a purinebase or a pyrimidine base, which may or may not be in the form ofderivative thereof.
 3. The process according to claim 2, wherein B isany base of hypoxanthine, adenine, guanine, uracil, thymine and cytosineor a derivative thereof.
 4. The process according to claim 1, wherein Ris any one of a hydrogen atom, an acyl group, an alkyl group, an aralkylgroup and a silyl group.
 5. The process according to claim 4, whereinthe acyl group is an acetyl group or a benzoyl group, and the aralkylgroup is a trityl group.
 6. The process according to claim 1, whereinthe eliminating group represented by either Y or X is any one of halogenatoms (exceeding a fluorine atom) and O-thiocarbonyl derivatives(residue).
 7. The process according to claim 1, wherein the protectedhydroxyl group in the case where either Y or X represents a protectedhydroxyl group is any one of an acyloxy group, an alkyloxy group, anaralkyloxy group and a silyloxy group.
 8. The process according to claim7, wherein the acyloxy group is an acetyloxy group or a benzoyloxygroup.
 9. The process according to claim 1, wherein hypophosphorous acidis in the form of a sodium salt.
 10. The process according to claim 1,wherein the radical reaction initiator is an azo compound.
 11. Theprocess according to claim 6, wherein the O-thiocarbonyl derivatives(residue) are O-phenoxythiocarbonyl, O-parafluorophenoxythiocarbonyl,O-methylthiothiocarbonyl, O-phenylthiothiocarbonyl andO-imidazolylthiocarbonyl group.
 12. The process according to claim 1,wherein in the general formula (II), B is an adenine, Y′ is a hydrogenatom, X′ is a hydrogen atom or a fluorine atom, R is a hydrogen atom ora hydroxy group-protecting group, and if R is the protecting group, thisgroup is further eliminated to produce ddA or FddA.
 13. The processaccording to claim 1, wherein the compound produced in claim 1 in whichB is a purine base or a derivative thereof, Y′ is a hydrogen atom, X′ isa hydroxyl group or a protected hydroxyl group, is subjected to at leastone step of the step of deprotecting the hydroxyl group, the step ofhalogenation at the 6-position, the step of amination at the 6-positionand the step of fluorination at the 2′-position to produce FddA.
 14. Theprocess according to claim 13, wherein said produced compound in which Bis an adenine, Y′ is a hydrogen atom, X′ is a hydroxyl group or aprotected hydroxyl group, is subjected to the step of fluorination atthe 2′-position, and if R is the protecting group, the compound isfurther subjected to the step of deprotection.
 15. The process accordingto claim 13, wherein said produced compound in which B is6-halogenopurine, Y′ is a hydrogen atom, and X′ is a hydroxyl group or aprotected hydroxyl group, is subjected to the step of fluorination atthe 2′-position and the step of amination at the 6′-position in thisorder or in the reverse order, and if R is the protecting group, thecompound is further subjected to the step of deprotection.
 16. Theprocess according to claim 13, wherein said produced compound in which Bis 6-hydroxypurine, Y′ is a hydrogen atom, and X′ is a hydroxyl group ora protected hydroxyl group, is subjected to the step of halogenation atthe 6-position to produce the compound substituted with a halogen at the6-position which is then subjected to the step of fluorination at the2′-position and the step of amination at the 6-position in this order orin the reverse order, and if R is the protecting group, the compound isfurther subjected to the step of deprotection, provided that if saidcompound has a protected hydroxyl group, its protecting group may beeliminated and then the compound may be subjected to the step ofhalogenation at the 6-position, and if said halogen-substituted compoundhas a protected hydroxyl group, the protecting group for said hydroxylgroup may be eliminated and then the compound may be subjected to thestep of amination at the 6-position.